A stereoscopic microscope as an example of a microscope apparatus can stereoscopically observe an object with protrusions and recesses as if the object is viewed by both eyes. Therefore, a distance relationship between a tool, such as tweezers, and an object can be easily recognized in an operation with the microscope. Thus, the stereoscopic microscope is particularly effective in a field that requires precise procedures, such as precision machinery industry and anatomy or surgery of living organisms. In such a stereoscopic microscope, an optical system that guides the luminous flux entering left and right eyes is at least partially separated to cause the optical axes to intersect over the surface of the object to obtain a parallax for stereoscopically observing the object. Enlarged images of the object viewed from different directions are created, and the images are observed through an eyepiece to stereoscopically view a minute object. An example of a typical configuration of the stereoscopic microscope includes a parallel stereoscopic microscope. The parallel stereoscopic microscope (parallel single-objective binocular microscope) includes one objective lens and two observation optical systems for right and left eyes arranged parallel to the optical axis of the objective lens. In this case, the objective lens that has brought the focus position in line with the surface of the object plays a role of guiding the parallel luminous flux to the following variable power lens groups for left and right eyes. The parallel luminous flux ejected from the objective lens is divided into two optical paths (variable power lens groups or observation optical systems) and is separately delivered to the left and right eyes.
In the parallel stereoscopic microscope, the observation optical system divides the light collected by the objective lens into two optical paths, and the effective diameter is about half the objective lens. Accordingly, the resolving power is also approximately halved, and the optical performance of the objective lens cannot be fully utilized. Therefore, a microscope apparatus is developed, in which incident effective diameters of left and right observation optical systems are differentiated to improve the resolving power of only an optical system of one side to acquire a high-resolution image (for example, see Patent Literature 1).